A pressure relieved piston rod seal for piston cylinders having tandem or multiple rod seals.
Hydraulic cylinders, for example, normally include a hydraulic cylinder having a pressure chamber and a piston having a head portion reciprocal in the cylinder chamber and a rod portion extending out of the cylinder through a bore generally including multiple annular rod seals. Various improvements have been made in the rod seals, however, the seals are still subject to failure from aging, frictional war and heat. In theory, the low pressure or redundant seal continues to seal the cylinder bore when the first or high pressure seal fails, however, it has been discovered that the use of multiple seals may actually contribute to the failure of the rod seals, as described herein.
Reciprocation of the piston rod portion in the cylinder bore results in heating of the sealing rings and the hydraulic fluid trapped in the channels enclosing the seals and between the seals around the piston rod. This heating results in expansion of the seals and the hydraulic fluid. The fluid pressure between the seals in the cylinder bore will, at times, exceed the pressure in the cylinder chamber. When this pressure exceeds the elastic limit of the seals, the seals fail. In the examination of such failures, it has been discovered that the high pressure seal closest to the pressure chamber is extruded between the piston rod and the cylinder bore toward the cylinder pressure chamber and the low pressure seal is extruded toward the exterior of the bore, resulting in the failure of both seals.
This problem has been solved in the piston rods seal of the present invention by utilizing two seals operating in tandem including a unidirectional high pressure seal which relieves the fluid pressure between the seals as described hereinbelow.